Step Needle for Intraosseous Access Device

ABSTRACT

Embodiments disclosed herein are directed to apparatus and methods for a stepped needle for an intraosseous device that uses the outer surface of the bone cortex as a reference point. Since the thickness of the bone cortex does not vary significantly between patients, the accuracy of needle placement can be improved. The device includes a needle with a stepped increase in outer diameter disposed along the needle shaft. The abrupt change in outer diameter provides a substantial increase in insertion force. In embodiments, the stepped increase prevents any further insertion into the bone cortex. Embodiments include a tapered needle lumen for medullary access confirmation and an overtube that is rotatably and slidably engaged to protect surrounding tissues and prevent needle stick injuries. Further, a needle hub can be rotatable or slidable, and can transition an overtube to an extended position to prevent accidental needle stick injuries.

PRIORITY

This application claims the benefit of priority to U.S. Provisional Application No. 62/907,450, filed Sep. 27, 2019, which is incorporated by reference in its entirety into this application.

SUMMARY

Placing an intraosseous (“I.O.”) device requires driving a needle and an obturator of an access assembly through the patient's skin and tissue until the needle tip is pressed against a surface of the bone cortex. Exemplary bones which can be accessed include the proximal tibia or humerus. The needle is then drilled, using a power driver (e.g. electrical or spring), manual awl, or the like, through the outer cortex of the bone until the tip enters the medullary cavity. The user then ceases drilling, and the obturator is removed leaving the hollow needle in place. The proximal needle hub is accessed and fluids can be introduced.

Currently, the user must make a subjective assessment of when the needle is correctly placed. The user “feels” the needle advance past the relatively hard and compact, cortex layer of the bone and penetrates into the relatively soft, medullary cavity of the bone. However, the relative density of the bone cortex compared with the medullary cavity can vary depending on the bone, size of medullary space, and the patient. Accordingly, the clinician relies on a subjective assessment of a “lack of resistance” in order to determine if the medullary cavity has been successfully accessed. Further, the user relies on a subjective assessment to ensure that the needle does not advance through the medullary space and penetrate a far wall of the medullary cavity. Some devices include a stopping feature that contacts a skin surface. However, skin and subcutaneous tissue thickness can vary greatly between patients, leading to missed placements.

Briefly summarized, embodiments disclosed herein are directed to apparatus and methods for a stepped needle for an intraosseous device that uses the outer surface of the bone cortex as a reference point. Since the thickness of the bone cortex does not vary significantly between patients, the accuracy of needle placement can be improved. The device includes a needle with a stepped increase in outer diameter disposed along the needle shaft. The abrupt change in outer diameter is sufficient to provide a substantial increase in insertion force. In an embodiment, the stepped increase in outer diameter prevents the needle from being inserted any further into the bone cortex. The distance from the needle tip to the stepped increase in outer diameter is sufficient to ensure the needle tip enters the medullary cavity while preventing impingement on a far wall of the medullary cavity.

Disclosed herein is a needle assembly for an intraosseous access system including, a needle supported by a needle hub and extending to a distal tip, and a stepped increase in diameter disposed on an outer surface of the needle at a predetermined distance from the distal tip, the stepped increase in diameter configured to penetrate a skin surface and abut against a bone cortex.

In some embodiments, the predetermined distance is configured to allow the distal tip to extend through the bone cortex and into a medullary cavity of a bone. The stepped increase in diameter is formed integrally with the needle. A distal surface of the stepped increase in diameter extends perpendicular to a longitudinal axis of the needle. A distal surface of the stepped increase in diameter extends at an angle to a longitudinal axis of the needle to define a tapered shape. The needle defines a lumen having a first needle lumen diameter disposed distally of the stepped increase in diameter, and a second needle lumen diameter disposed proximally of the stepped increase in diameter, the second needle lumen diameter being larger than the first needle lumen diameter. In some embodiments, the needle assembly for an intraosseous access system further includes a third needle lumen diameter disposed proximally of the second needle lumen diameter, the third needle lumen diameter being less than the second needle lumen diameter to define a bulged portion in the needle.

In some embodiments, the needle assembly further includes an obturator disposed within the needle lumen, an outer diameter of the obturator being equal to, or less than, the first needle lumen diameter. In some embodiments, the needle assembly further includes an overtube engaged with an outer surface of the needle, a distal tip of the overtube defining a portion of the stepped increase in diameter. A longitudinal length of the overtube is less than a longitudinal length of a shaft of the needle, the overtube being adhered to the outer surface of the needle to form a collar. The overtube is slidably or rotatably engaged with the needle.

In an embodiment, the overtube includes a metal, alloy, plastic, polymer, composite, or carbon-based composite material. The overtube includes a first material, and a second material different from the first material. The first material is a relatively softer material and can elastically or plastically deform, the second material is a harder material and can be resistant to any elastic or plastic deformation. The overtube is formed of concentric tubes including a first tube formed of one of the first material or the second material and disposed adjacent the needle, and a second tube disposed on an outer surface of the first tube and formed of one of the first material or the second material. The overtube is formed of adjacent tubes including a first tube formed of the first material and disposed distally of a second tube formed of the second material. A first portion of the overtube is formed the first material and extends annularly about the needle between 1° and 359°, and a second portion of the overtube is formed of the second material and extends annularly about the needle between 1° and 359°. The distal tip of the overtube is configured to blunt and increase in diameter on contact with a surface of the bone cortex.

In some embodiments, a proximal end of the overtube abuts against the needle hub to prevent further longitudinal movement of the distal tip of the needle. A first diameter of the needle hub is between 1 cm and 3 cm. The needle hub includes a flared portion extending to a second diameter, the second diameter being greater than the first diameter. The needle hub includes a proximal housing slidably or rotatably engaged with a distal housing. In some embodiments, the needle hub includes a biasing member configured to bias the distal housing towards a proximal position relative to the proximal housing. The distal housing includes a distal face configured to engage a skin surface. The overtube is slidably engaged with the needle between a retracted position and an extended position. The distal tip of the overtube extends distally of the distal tip of the needle in the extended position. In some embodiments, the needle assembly further includes an overtube biasing member configured to bias the overtube towards the extended position. In some embodiments, the needle assembly further includes a locking mechanism configured to retain the overtube in the retracted position when in a locked configuration.

In some embodiments, the needle assembly further includes an actuator configured to transition the locking mechanism between the locked configuration and an unlocked configuration. The actuator includes rotating or sliding the proximal housing relative to the distal housing. The overtube biasing member is configured to prevent the overtube from transitioning from the extended position to the retracted position. In some embodiments, the needle assembly further includes an abutment configured to engage the overtube in the extended position and prevent the overtube transitioning from the extended position to the retracted position. In some embodiments, one of the needle or the overtube includes graduated markings.

Also disclosed is a method of accessing a medullary cavity including, penetrating a bone cortex with a distal tip of a needle, the needle including a stepped increase in outer diameter disposed at a predetermined distance from the distal tip, the predetermined distance being greater than a thickness of the bone cortex, abutting the stepped increase in outer diameter against a surface of the bone cortex to prevent further distal advancement of the distal tip, and accessing the medullary cavity.

In some embodiments, the method further includes withdrawing an obturator from a lumen of the needle until a distal tip of the obturator is proximal of a stepped increase in diameter of the lumen to allow a proximal blood flow to be observed and confirm medullary access. An overtube is slidably or rotatably engaged with the needle, a distal surface of the overtube defining a portion of the stepped increase in outer diameter. In some embodiments, the method further includes abutting a proximal end of the overtube against a needle hub to prevent further distal advancement of the distal tip of the needle. In some embodiments, the method further includes abutting a distal surface of a distal housing of a needle hub against a skin surface, the distal housing slidably or rotatably engaged with a proximal housing to allow the distal tip to continue to advance distally to access the medullary cavity. In some embodiments, the method further includes biasing the distal housing towards a distal position relative to the proximal housing.

In some embodiments, the method further includes transitioning the overtube between a retracted position, where a distal surface of the overtube is disposed at a predetermined distance from the distal tip of the needle, and an extended position where a distal surface of the overtube is disposed distally of the distal tip of the needle. In some embodiments, the method further includes biasing the overtube to the extended position. In some embodiments, the method further includes locking the overtube in the retracted position. In some embodiments, the method further includes sliding or rotating the proximal housing relative to the distal housing to unlock the overtube and transition the overtube from the retracted position to the extended position. In some embodiments, the method further includes engaging an abutment with a portion of the overtube to prevent the overtube transitioning from the extended position to the retracted position.

DRAWINGS

A more particular description of the present disclosure will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. Example embodiments of the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

FIG. 1 illustrates an exploded view of an embodiment of an intraosseous access system, wherein an access assembly subset of the system is depicted slightly enlarged and in elevation, and an automated driver component is depicted in perspective, in accordance with embodiments disclosed herein.

FIG. 2 illustrates the access assembly of FIG. 1 accessing a medullary cavity of a patient, in accordance with embodiments disclosed herein.

FIG. 3 illustrates a side profile view of an access assembly including a stepped portion, in accordance with embodiments disclosed herein.

FIG. 4 illustrates a perspective view of an access assembly including a stepped portion, in accordance with embodiments disclosed herein.

FIGS. 5A-5L illustrate cross-sectional views of a stepped portion of the access assembly, in accordance with embodiments disclosed herein.

FIGS. 6A-6B illustrate cross-sectional views of an access assembly, in accordance with embodiments disclosed herein.

FIGS. 7A-7B illustrate perspective views of an access assembly, in accordance with embodiments disclosed herein.

FIGS. 8A-8D illustrate cross-sectional views of an access assembly, in accordance with embodiments disclosed herein.

DESCRIPTION

Before some particular embodiments are disclosed in greater detail, it should be understood that the particular embodiments disclosed herein do not limit the scope of the concepts provided herein. It should also be understood that a particular embodiment disclosed herein can have features that can be readily separated from the particular embodiment and optionally combined with or substituted for features of any of a number of other embodiments disclosed herein.

Regarding terms used herein, it should also be understood the terms are for the purpose of describing some particular embodiments, and the terms do not limit the scope of the concepts provided herein. Ordinal numbers (e.g., first, second, third, etc.) are generally used to distinguish or identify different features or steps in a group of features or steps, and do not supply a serial or numerical limitation. For example, “first,” “second,” and “third” features or steps need not necessarily appear in that order, and the particular embodiments including such features or steps need not necessarily be limited to the three features or steps. Labels such as “left,” “right,” “top,” “bottom,” “front,” “back,” and the like are used for convenience and are not intended to imply, for example, any particular fixed location, orientation, or direction. Instead, such labels are used to reflect, for example, relative location, orientation, or directions. Singular forms of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise.

With respect to “proximal,” a “proximal portion” or a “proximal end portion” of, for example, a needle disclosed herein includes a portion of the needle intended to be near a clinician when the needle is used on a patient. Likewise, a “proximal length” of, for example, the needle includes a length of the needle intended to be near the clinician when the needle is used on the patient. A “proximal end” of, for example, the needle includes an end of the needle intended to be near the clinician when the needle is used on the patient. The proximal portion, the proximal end portion, or the proximal length of the needle can include the proximal end of the needle; however, the proximal portion, the proximal end portion, or the proximal length of the needle need not include the proximal end of the needle. That is, unless context suggests otherwise, the proximal portion, the proximal end portion, or the proximal length of the needle is not a terminal portion or terminal length of the needle.

With respect to “distal,” a “distal portion” or a “distal end portion” of, for example, a needle disclosed herein includes a portion of the needle intended to be near or in a patient when the needle is used on the patient. Likewise, a “distal length” of, for example, the needle includes a length of the needle intended to be near or in the patient when the needle is used on the patient. A “distal end” of, for example, the needle includes an end of the needle intended to be near or in the patient when the needle is used on the patient. The distal portion, the distal end portion, or the distal length of the needle can include the distal end of the needle; however, the distal portion, the distal end portion, or the distal length of the needle need not include the distal end of the needle. That is, unless context suggests otherwise, the distal portion, the distal end portion, or the distal length of the needle is not a terminal portion or terminal length of the needle.

As shown in FIG. 1, and to assist in the description of embodiments described herein, a longitudinal axis extends substantially parallel to an axial length of a needle 204 extending from the driver 101. A lateral axis extends normal to the longitudinal axis, and a transverse axis extends normal to both the longitudinal and lateral axes.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art.

The present disclosure relates generally to intraosseous (“I.O.”) access devices, systems, and methods thereof. FIG. 1 shows an exploded view of an exemplary embodiment of an intraosseous access system 100, with some components thereof shown in elevation and another shown in perspective. The intraosseous access system 100 can be used to penetrate skin and underlying hard bone for intraosseous access, such as, for example to access the marrow of the bone and/or a vasculature of the patient via a pathway through an interior of the bone.

In an embodiment, the system includes a driver 101 and an access assembly 109. The driver 101 can be used to rotate the access assembly 109 into a bone of a patient. In embodiments, the driver 101 can be automated or manual. In an embodiment, the driver 101 is an automated driver 108. For example, the automated driver 108 can be a drill that achieves high rotational speeds.

The intraosseous access system 100 can further include an obturator assembly 102, a shield 105, and a needle assembly 202, which may be referred to, collectively, as the access assembly 109. The access assembly 109 may also be referred to as an access system. The obturator assembly 102 is referred to as such herein for convenience. In an embodiment, the obturator assembly 102 includes an obturator 104. However, in some embodiments, the obturator 104 may be replaced with a different elongated medical instrument. As used herein, the term “elongated medical instrument” is a broad term used in its ordinary sense that includes, for example, such devices as needles, cannulas, trocars, obturators, stylets, and the like. Accordingly, the obturator assembly 102 may be referred to more generally as an elongated medical instrument assembly. In like manner, the obturator 104 may be referred to more generally as an elongated medical instrument.

In an embodiment, the obturator assembly 102 includes a coupling hub 103 that is attached to the obturator 104 in any suitable manner (e.g., one or more adhesives or overmolding). The coupling hub 103 can be configured to interface with the driver 101. The coupling hub 103 may alternatively be referred to as an obturator hub 103 or, more generally, as an elongated instrument hub 103.

In an embodiment, the shield 105 is configured to couple with the obturator 104. The coupling can permit relative longitudinal movement between the obturator 104 and the shield 105, such as sliding, translating, or other movement along an axis of elongation (i.e., axial movement), when the shield 105 is in a first operational mode, and can prevent the same variety of movement when the shield 105 is transitioned to a second operational mode. For example, as further discussed below, the shield 105 may couple with the obturator 104 in a manner that permits longitudinal translation when the obturator 104 maintains the shield 105 in an unlocked state, and when the obturator 104 is moved to a position where it no longer maintains the shield in the unlocked state, the shield 105 may automatically transition to a locked state in which little or no translational movement is permitted between the shield 105 and the obturator 104. Stated otherwise, the shield 105 may be longitudinally locked to a fixed or substantially fixed longitudinal orientation relative to the obturator 104 at which the shield 105 inhibits or prevents inadvertent contact with a distal tip of the obturator. In various embodiments, the shield 105 may be configured to rotate relative to the obturator 104 about a longitudinal axis of the obturator 104 in one or more of the unlocked or locked states.

With continued reference to FIG. 1, the needle assembly 202 is referred to as such herein for convenience. In an embodiment, the needle assembly 202 includes a needle 204. However, in various other embodiments, the needle 204 may be replaced with a different instrument, such as, for example, a cannula, a tube, or a sheath, and/or may be referred to by a different name, such as one or more of the foregoing examples. Accordingly, the needle assembly 202 may be referred to more generally as a cannula assembly or as a tube assembly. In like manner, the needle 204 may be referred to more generally as a cannula.

In an embodiment, the needle assembly 202 includes a needle hub 203 that is attached to the needle 204 in any suitable manner. The needle hub 203 can be configured to couple with the obturator hub 103 and may thereby be coupled with the driver 101, as further discussed below. The needle hub 203 may alternatively be referred to as a cannula hub 203.

In an embodiment, the shield 105 is configured to couple with the needle hub 203. The coupling can prevent relative axial or longitudinal movement between the needle hub 203 and the shield 105, such as sliding, translating, or the like, when the shield 105 is in the first operational mode, and can permit the shield 105 to decouple from the needle hub 203 when the shield 105 is transitioned to the second operational mode. For example, as further discussed below, the shield 105 may couple with the needle hub 203 so as to be maintained at a substantially fixed longitudinal position relative thereto when the obturator 104 maintains the shield 105 in the unlocked state, and when the obturator 104 is moved to a position where it no longer maintains the shield in the unlocked state, the shield 105 may automatically transition to a locked state relative to the obturator 104, in which state the shield 105 also decouples from the needle hub 203.

In an embodiment, the shield 105 can be coupled with the obturator 104, the obturator 104 can be inserted into the needle 204, and the obturator hub 103 can be coupled to the needle hub 203 to assemble the access assembly 109. In an embodiment, a cap 107 may be provided to cover at least a distal portion of the needle 204 and the obturator 104 prior to use of the access assembly 109. For example, in an embodiment, a proximal end of the cap 107 can be coupled to the obturator hub 103.

With continued reference to FIG. 1, the automated driver 108 may take any suitable form. The driver 108 may include a handle 110 that may be gripped by a single hand of a user. The driver 108 may further include an actuator 111 of any suitable variety via which a user may selectively actuate the driver 108 to effect rotation of a coupling interface 112. For example, the actuator 111 may comprise a button, as shown, or a switch or other mechanical or electrical element for actuating the driver 108. In an embodiment, the coupling interface 112 is formed as a socket 113 that defines a cavity 114. The coupling interface 112 can be configured to couple with the obturator hub 103. In an embodiment, the socket 113 includes sidewalls that substantially define a hexagonal cavity into which a hexagonal protrusion of the obturator hub 103 can be received. Other suitable connection interfaces are contemplated.

The automated driver 108 can include an energy source 115 of any suitable variety that is configured to energize the rotational movement of the coupling interface 112. For example, in some embodiments, the energy source 115 may comprise one or more batteries that provide electrical power for the automated driver 108. In other embodiments, the energy source 115 can comprise one or more springs (e.g., a coiled spring) or other biasing member that may store potential mechanical energy that may be released upon actuation of the actuator 111.

The energy source 115 may be coupled with the coupling interface 112 in any suitable manner. For example, in an embodiment, the automated driver 108 includes an electrical, mechanical, or electromechanical coupling 116 to a gear assembly 117. In some embodiments, the coupling 116 may include an electrical motor that generates mechanical movement from electrical energy provided by an electrical energy source 115. In other embodiments, the coupling 116 may include a mechanical linkage that mechanically transfers rotational energy from a mechanical (e.g., spring-based) energy source 115 to the gear assembly 117. The automated driver 108 can include a mechanical coupling 118 of any suitable variety to couple the gear assembly 117 with the coupling interface 112. In other embodiments, the gear assembly 117 may be omitted.

In embodiments, the automated driver 108 can rotate the coupling interface 112, and thereby, can rotate the access assembly 109 at rotational speeds significantly greater than can be achieved by manual rotation of the access assembly 109. For example, in various embodiments, the automated driver 108 can rotate the access assembly 109 at speeds of between 200 and 3,000 rotations per minute. However, greater or lesser rotations per minute are also contemplated.

Further details and embodiments of the intraosseous access system 100 can be found in patent application publications: WO 2018/075694, WO 2018/165334, WO 2018/165339, and US 2018/0116693, each of which is incorporated by reference in its entirety into this application.

FIG. 2 shows an exemplary access assembly 109, which includes an obturator assembly 102 and a needle assembly 202. The access assembly 109 is disposed within a patient with a tip 205 of the needle 204 extending through the skin surface 70, subcutaneous tissues 75, bone cortex 80, and enters the medullary cavity 90. The needle 204 further includes an obturator 104 disposed within a lumen thereof to prevent tissue, bone fragments and the like, entering and obstructing the needle lumen.

As shown in FIGS. 2-4, the needle 204 further includes a stepped portion (“step”) 254 disposed annularly about an outer surface of the needle shaft 250 and defining an increase in outer diameter of the needle 204. The stepped portion 254 is positioned at a predefined distance (x) from the needle tip 205. The step 254 extends radially from the needle shaft 250 to provide an increase in outer diameter of the needle shaft 250. The step 254 provides an increase in resistance as the needle 204 is driven into the bone cortex 80. In an embodiment, the step 254 provides sufficient change in resistance to indicate to a user that the step 254 has contacted the outer surface of the bone cortex 80, indicating that the needle bevel is within the medullary cavity 90, as shown in FIG. 2. In an embodiment, the step 254 prevents any further insertion of the needle 204 into the bone cortex 80. In an embodiment, as shown in FIG. 4, the needle 204 includes an overtube 264 that provides the step 254, as will be described in more detail herein.

In an embodiment, the needle 204, overtube 264, or combinations thereof, include graduated markings 266 to indicate a depth of the needle tip 205 and guide the user as to when the needle tip 205 is correctly placed. In an embodiment, the overtube 264 can be formed of a metal, alloy, plastic, polymer, composite, carbon-based composite, combinations thereof, or the like. In an embodiment, a first portion of the overtube 264 can be formed of a first material, and a second portion of the overtube 264 can be formed of a second material different from the first material. In an embodiment the first material and the second material can display different mechanical properties. In an embodiment, the first material can be formed of a metal, alloy, or the like, and the second material can be formed of a plastic, polymer, or the like.

FIGS. 5A-5H show close up views of embodiments of the step 254. It will be appreciated the features of these embodiments can be used in any combination without limitation and fall within the scope of the present invention. As shown in FIG. 5A, in an embodiment, the step 254 is formed integrally with the needle shaft 250. As such, the needle 204 includes a distal portion 274 disposed distally of the step 254 and defines a first outer diameter, and a proximal portion 276 disposed proximally of the step 254 and defining a second outer diameter. The first outer diameter being less than the second outer diameter to define the step 254. A first needle lumen diameter 268 defines a constant diameter both distally and proximally of the step 254. Accordingly, a wall thickness of the proximal portion 276 of the needle 204 is greater than a wall thickness of the distal portion 274 of the needle 204.

As shown in FIG. 5B, in an embodiment, the step 254 is formed integrally with the needle shaft 250. As such, the needle 204 includes a distal portion 274 disposed distally of the step 254 and defines a first outer diameter, and a proximal portion 276 disposed proximally of the step 254 and defining a second outer diameter. The first outer diameter being less than the second outer diameter to define the step 254. A needle lumen extending through the distal portion defines a first diameter 268, and a needle lumen extending through the proximal portion defines a second diameter 278, the second lumen diameter 278 being greater than the first lumen diameter 268. Accordingly, a wall thickness of the needle 204 maintains a substantially constant thickness.

As shown in FIG. 5C, in an embodiment, the needle 204 defines a lumen including a first lumen diameter 268 and a second lumen diameter 278, and a substantially constant wall thickness, as described herein in reference to FIG. 5B. The step 254 defines a tapered outer profile to provide an increase in outer diameter and to facilitate insertion of the needle through subcutaneous tissues 75. The step 254 provides an increase in resistance when the step 254 contacts the bone cortex 80. In an embodiment, a portion of the step 254 can be inserted within the bone cortex 80. The needle lumen also includes a tapered transition portion 256, adjacent the step 254 and disposed between the distal portion 274 of the needle 204, which defines a first lumen diameter 268, and the proximal portion 276 of the needle 204, which defines a second lumen diameter 278.

In an embodiment, the needle 204 can include a third portion (not shown) disposed proximally of the proximal portion 276 that defines a needle lumen having a first diameter 268, i.e. a needle lumen that is less that the second lumen diameter 278. As such the proximal portion 276 defines a “bulged” portion disposed at a predetermined distance (x) from the needle tip, as described herein. In an embodiment, the predetermined distance (x) can be between 1 cm and 3 cm, however other predetermined distances are also possible and within the scope of the invention. In an embodiment, the bulged proximal portion 276 can include a stepped, tapered, or rounded increase in diameter and decrease in diameter, back to the diameter of the distal portion 274.

In the embodiments shown in FIGS. 5B and 5C, the needle lumen facilitates medullary cavity access confirmation. In use, the needle 204 is inserted through the bone cortex 80 until the step 254 increases resistance. A user can then confirm the needle bevel is disposed within the medullary cavity by partially withdrawing the obturator 104 until a distal end thereof is proximal of the step 254. As shown in FIG. 5D, blood can then flow proximally through the needle lumen, past the obturator 104, to a needle hub where the blood flow can be observed to confirm medullary cavity access. If the needle tip 205 has not accessed the medullary cavity 90, a reduced or absent blood flow will be observed. In which case the obturator 104 can be reinserted with minimal risk of contamination, and insertion of the access assembly 109 can continue through the bone cortex 80. In an embodiment, the tapered transition portion 256 of the needle lumen can facilitate reinsertion of the obturator 104 within the distal portion of the needle lumen.

As shown in FIGS. 5E-5F, in an embodiment, the needle 204 defines a substantially constant outer diameter, a constant wall thickness, and a constant lumen diameter. The needle 204 further includes an overtube 264 disposed on an outer surface of the needle 204 and defines an overtube wall thickness that defines the step 254. In an embodiment, a distal end of the overtube 264 extends to a point that is proximal of the needle tip 205. In an embodiment, a distal end of the overtube 264 extends to a point that is a predetermined distance (x) from the needle tip 205. As noted, the predetermined distance (x) can be between 1 cm and 3 cm, however other predetermined distances are also possible and within the scope of the invention, as described herein. As shown in FIG. 5F, the distal end of the overtube 264 can be tapered to facilitate insertion of the needle through tissues 70, 75.

In an embodiment, the overtube 264 is attached to the needle shaft by adhesive, welding, bonding, crimping or the like. Accordingly, the overtube 264 is fixed and unable to move relative to the needle 204. In an embodiment, the overtube 264 can extend over a portion of the needle 204. In an embodiment, a proximal end of the overtube 264 can extend to a point that is distal of the needle hub 203. In an embodiment, the overtube 264 can define a collar that is attached to the needle shaft as described herein.

In an embodiment, the overtube 264 is slidably engaged with the needle 204 and can be selectively secured in place. The position of a distal end of the overtube 264 can be adjusted relative to the needle tip 205 to a preferred distance along the longitudinal axis. The user can select a predetermined distance (x) depending on the type of target bone, the procedure, or age or health of the patient, or the like. For example, a predetermined distance (x) of 10 mm-15 mm would be preferable for smaller, pediatric patients, where a distance of 15 mm-30 mm would be preferable for larger, adult patients.

In an embodiment, the overtube 264 is rotatably engaged with the needle 204 about the longitudinal axis. This allows the needle 204 to spin freely while the overtube 264 remains substantially stationary. In an embodiment, the needle 204 can be drilled through the bone cortex 80 and the overtube 264 protects the surrounding tissues 70, 75 from twisting about the needle 204 as the needle spins. The overtube 264 therefore protects the tissues 70, 75 from damage and irritation. In an embodiment, the overtube 264 can be both slidably and rotatably engaged with the needle 204. Accordingly, the user can select a predetermined distance (x) between the distal end of the overtube 264 and the needle tip 205. Further the overtube can protect any surrounding tissue 70, 75 as the needle is drilled into the bone cortex 80.

In an embodiment, as shown in FIGS. 5G and 5H, the needle 204 includes both a stepped portion 254, for example as described herein in reference to FIGS. 5A-5D, as well as an overtube 264. The distal end of the overtube 264 can align with the stepped portion 264. In an embodiment, the distal end of the overtube 264 can be positioned proximally of the stepped portion 254 to provide a second step (not shown). For example, the first step 254 can indicate that the user is approaching the predetermined depth. A user can then continue to insert the access assembly 109, including the first step, through the bone cortex 80, until a second step (not shown) contacts the bone cortex indicating that the desired depth is reached, or preventing any further insertion of the access assembly 109.

As shown in FIGS. 51-5L, the overtube 264 can include a first material 282 and a second material 284. In an embodiment, the overtube 264 can be formed of one or more concentric tubes of one or more different materials, e.g. as shown in FIGS. 51-5J. In an embodiment, the overtube 264 can be formed of one or more adjacent tubes of one or more different materials, disposed along the longitudinal axis, e.g. FIG. 5K. In an embodiment, the overtube 264 can include different adjacent portions formed of one or more materials.

As shown in FIGS. 51-5J, in an embodiment, the first material is overmolded on to the second material 284, which is disposed adjacent the needle shaft 250, forming a tube thereabout. In an embodiment the first material 282 can be a plastic, polymer, or the like and the second material 284 can be a metal, alloy, or the like. In an embodiment, the first material 282 can display softer material properties or can elastically or plastically deform. In an embodiment, the second material 284 can display harder or resilient material properties and can be resistant to any elastic or plastic deformation. In an embodiment, as shown in FIG. 5J, the tube of a first material 282 can be disposed adjacent the needle shaft 250 and a tube of the second material 284 can be disposed thereover, substantially along an outer surface of the overtube 264.

In an embodiment, the second material 284 can provide structural support to overtube while the first material 282 can deform to increase the outer diameter of the overtube as it is urged against the bone cortex 80. To note the first material 282 can be sufficiently resilient to penetrate the skin surface tissues 70, 75 without deforming but can deform slightly, when urged against the bone cortex 80. Further, the relatively softer first material 282 can be configured to mitigate trauma to the bone cortex 80 as the needle 204 is rotated.

In an embodiment, a distal tip of the overtube 264, forming the stepped increase in diameter 254 can be formed of the first, relatively softer material 282. The tapered shape can facilitate penetrating the skin surface tissues 70, 75. Then, when the tapered stepped increase in diameter 254 contacts the relatively hard bone cortex 80, the tapered shape can deform and “mushroom” out, to abut against the bone cortex and provide an increase in resistance to distal advancement, as described herein. In an embodiment, the distal tip can mushroom out to a diameter that is greater than the outer diameter of the overtube 264 to provide a greater resistance to further distal advancement.

In an embodiment, as shown in FIG. 5K, the overtube 264 can be formed of one or more adjacent tubes of one or more different materials, disposed along the longitudinal axis. For example, the overtube 264 can be formed of a second, relatively harder material 284 and include a first, relatively softer material 282 disposed at a distal tip and forming the stepped increase in diameter 254. In an embodiment, the distal tip formed of the first material 282 can define a stepped increase in diameter 254 extending perpendicular to the longitudinal axis, or can define a tapered stepped increase in diameter 254, as described herein. The distal tip formed of the first material 282 can mitigate trauma to the bone cortex 80 as the overtube 264 is urged distally. In an embodiment, the distal tip formed of the first material 282 can deform, blunt, or “mushroom,” to provide an increase in outer diameter, an increase resistance to further distal advancement, cushion the impact of the overtube 264 against the bone cortex, or combinations thereof.

In an embodiment, as shown in FIG. 5L, a first side wall portion of the overtube 264 can be formed of a first material 282 and a second side wall portion of the overtube 264 can be formed of a second material 284. In an embodiment, each of the first side wall portion or the second side wall portion can extend along a longitudinal length of the overtube 264 from a proximal end 280 to the distal end, adjacent the stepped increase in diameter 254. In an embodiment, one of the first side wall portion or the second side wall portion can extend about the longitudinal axis between 1° and 360°. However, greater or lesser degrees are also contemplated. In an embodiment, the overtube 264 can be formed of a first half, extending about the longitudinal axis of the needle 204 by 180° and formed of a first material 282, a second half, extending about the longitudinal axis of the needle 204 by 180° and formed of a second material 284.

In an embodiment, the overtube 264 can be formed of a first quarter extending about the longitudinal axis of the needle 204 by 90° and formed of a first material 282, a second quarter disposed adjacent the first quarter, extending about the longitudinal axis of the needle 204 by 90° and formed of a second material 284, a third quarter disposed adjacent the second quarter, and extending about the longitudinal axis of the needle 204 by 90° and formed of a first material 282, and a fourth quarter disposed adjacent the third quarter, and extending about the longitudinal axis of the needle 204 by 90° and formed of a first material 282. It will be appreciated however, that other combinations of materials, and annular extensions, i.e. between 1° and 360°, of the different portions of the overtube 264 are also contemplated. In an embodiment, the overtube 264 can include a distal tip portion extending annularly about the needle 204 and formed of the first material 282. The distal tip portion can be configured to deform when contacting the bone cortex, as described herein.

In an embodiment, as shown in FIGS. 6A-6B, the overtube 264 can be both slidably and rotatably engaged as described herein. The distal end of the overtube 264 can longitudinally align with one of the needle tip 205, the needle bevel, or a proximal edge of the needle bevel. The overtube 264 and needle 204 can then be inserted through the skin 70 and subcutaneous tissues 75 until the distal end of the overtube 264 contacts a surface of the bone cortex 80. The needle 204 can then be rotated and drilled into the bone cortex 80 while the overtube 264 can remain substantially stationary, and protects the surrounding tissues 70, 75 from twisting about needle 204 as it spins. Advantageously, the overtube 264 being rotatably engaged with the needle 204 can allow the needle to rotate freely, while the overtube 264, or more specifically, the stepped increase in diameter 254 remains substantially stationary against the surface of the bone cortex 80. This can mitigate any friction or trauma of the bone cortex 80 by mitigating any movement of stepped increase in diameter 254 relative to the surface of the bone cortex 80. The needle 204 then advances distally, through the over tube 264 and through the bone cortex 80, until a proximal end 280 of the overtube 264 contacts a needle hub 203, preventing any further advancement of the needle 204 relative to the overtube 264. It will be appreciated that when the proximal end 280 of the overtube 264 contacts the needle hub 203, the distal end of the overtube 264 will be at a predetermined distance (x) from the needle tip 205. The predetermined distance (x) being sufficient to allow the needle bevel to enter the medullary cavity 90, without the needle tip 205 contacting a far wall of the medullary cavity 90.

With continuing reference to FIGS. 6A-6B, in an embodiment, when the needle is to be removed, the needle 204 can be retracted through the bone cortex 80 and into the overtube 264 such that a needle tip 205 is disposed within the lumen of the overtube 264. Optionally, the needle 204 and overtube 264 can then be locked in place relative to each other when the needle tip 205 is disposed within the lumen of the overtube 264. The needle 204 and overtube 264 can then be withdrawn from the tissues 70, 75. Accordingly, the overtube 264 provides a safety cover for the needle 204, preventing accidental needle stick injuries once the needle is removed from the patient.

As shown in FIGS. 7A-7B, in an embodiment, an access assembly 309 can include a needle hub 203 that defines an increased diameter (d1), extending perpendicular to a longitudinal axis of the needle 204. In an embodiment, a diameter (d1) of the needle hub 203 can be between 1 cm and 3 cm although greater or lesser diameters are also contemplated. Advantageously, the needle hub 203 with the increased diameter (d1) can provide increased leverage for a user to grasp the needle hub 203 and urge the needle 204 through the bone cortex 80 by hand, or remove the needle assembly 202 by hand after the procedure is complete. The increased hub diameter can be of importance if the driver 101 fails to operate, runs out of power, or if the user is able to determine access to medullary cavity 90 more accurately by urging the needle 204 by hand, through a remaining distance of bone cortex. For example, a user may use the driver 101 to drill the needle 204 through a majority of the bone cortex 80 and then detach the access assembly 109 and drive the needle 204 the remainder of the distance by hand in order to “feel” medullary cavity access more accurately. Further, the increased hub diameter can be important to allow a user to remove the needle 204 from the bone cortex 80 without having to attach a secondary device, e.g. syringe, hemostats, or the like, to the needle hub 203 to facilitate removal of the needle 204.

In an embodiment, the needle hub 203 can include one or more flared portions 303, for example a distal flared portion 303A and a proximal flared portion 303B. The flared portion 303 can extend annularly about the hub and provide an increased diameter (d2) relative to the diameter (d1) of the needle hub 203. Advantageously, the flared portion 303 can provide support for a user when urging the needle hub 203 along the longitudinal axis in either of the proximal or distal directions. Further the flared portion 303 can guide a user's fingers towards a longitudinal midpoint of the needle hub 203 and provide a secure grasp of the needle hub 203. This can be important in an emergency situations, where a user, who is often wearing gloves, would need to grasp the hub 203 rapidly and apply significant force to the needle hub 203, while avoiding slipping.

In an embodiment, the needle hub 203 can include a distal housing 304A and a proximal housing 304B that are slidable engaged with each other, for example, in a telescoping manner. As shown in FIG. 7A, an outer diameter of the proximal housing 304A can be equal to an inner diameter of the proximal housing 304B to allow the distal housing 304A to slide into a cavity defined by the proximal housing 304B. It will be appreciated that other configurations of housings 304A, 304B are also contemplated, for example the proximal housing 304B being received within the distal housing 304A.

Advantageously, the proximal housing 304B can spin about the longitudinal axis independently of the distal housing 304A. As such, as the access assembly 309 advances into the patient, a distal face 306 of the distal housing 304A can contact a skin surface of the patient. The distal face 306 of the distal housing 304A can rest in a substantially stationary position against the skin surface, allowing the proximal housing 304B and/or needle 204 to rotate about the longitudinal axis until the medullary cavity is accessed. The distal housing 304A can mitigate friction between the access assembly 309 and the skin surface, preventing friction burns, or similar trauma.

In an embodiment, the distal housing 304A can slide independently of the proximal housing 304B and/or needle 204, along the longitudinal axis. In an embodiment, the needle hub 204 can further include a biasing member, e.g. compression spring, or the like, configured to bias the distal housing 304A towards a longitudinally distal position. In an embodiment, when a distal face 306 of the distal housing 304A contacts a skin surface of the patient, the proximal housing 304B and/or the needle 204 can continue to advance distally, along the longitudinal axis until the medullary cavity 90 is accessed. The distal housing 304A can rest on a skin surface and remain substantially stationary preventing compression or trauma of the surface tissues 70, 75 disposed between the distal face 306 and the bone cortex 80. This can be important where a thickness of the surface tissues 70, 75 can vary significantly between different patients.

Further, the distal face 306 can align with the skin surface 70 to stabilize the needle assembly 202 once the needle 204 has been placed correctly. In an embodiment, a stabilizing device can be attached to the needle hub 203 or distal housing 304A to further stabilize the needle assembly 202 relative to the skin surface 70. The biasing member disposed within the needle hub can be configured to apply sufficient pressure to the distal housing 304A to urge the distal face 306 against the skin surface 70 and stabilize the needle hub 204, without compressing the surface tissues 70, 75 between the distal face 306 and the bone cortex 80. In an embodiment, the distal face 306 can include an adhesive or the like to further stabilize the needle assembly 202 with the skin surface 70.

As shown in FIGS. 8A-8D, in an embodiment, the access assembly 309 can include an overtube 364 slidably engaged with an outer surface of the needle 204 and defining a thickness to define a stepped portion 254 at a distal end thereof. To note, the overtube 364 can allow the needle 204 to rotate independently of the overtube 364, as described herein. In an embodiment, the overtube 364 can be slidable along a longitudinal axis of the needle 204 between a retracted position (FIG. 7A) and an extended position (FIG. 7B).

In an embodiment, with the overtube 364 in the retracted position, a predetermined distance (x) between a distal tip of the overtube 364 that defines a stepped outer diameter 254 and a distal tip of the needle 205 can be sufficient to allow a bevel of the needle to access the medullary cavity 90. In the extended position, a distal tip of the overtube 364 can extend distally of the distal tip 205 of the needle 204. The needle hub 203 can include an overtube biasing member 366, e.g. a compression spring or the like, configured to bias the overtube 364 towards an extended position.

The needle hub 203 can further include a locking mechanism 340 configured to selectively retain the overtube 364 in a retracted position. As shown, the locking mechanism is disposed at a mid-section of the overtube 364, however, it will be appreciated that other configurations of locking mechanism 340 are also contemplated including disposing towards a proximal end. In the retracted position, the locking mechanism 340 can inhibit proximal movement of the overtube 364 relative to the needle 204 to maintain the predetermined distance (x) between the stepped portion 254 and the needle tip 205. Further, the locking mechanism in the locked configuration, can retain the overtube 364 to prevent distal advancement of the overtube 364 relative to the needle 204. In an embodiment, the locking mechanism 340 can be transitioned from the locked configuration to the unlocked configuration to allow the overtube biasing member 366 to urge the overtube 364 to the extended position. Advantageously, in the extended position, the overtube 364 can prevent accidental needle stick injuries when the needle 204 is withdrawn proximally from the patient.

In an embodiment, the locking mechanism 340 can be transitioned from the locked configuration to the unlocked configuration by rotating the proximal housing 304B relative to the distal housing 304A in one of a clockwise or anti-clockwise direction. Advantageously, the proximal housing 304B can include a gripping feature 308 configured to facilitate grasping the proximal housing 304B and rotating the proximal housing about the longitudinal axis. Exemplary gripping features 308 can include grooves, ridges, or similar structures, and/or can include different materials disposed on a surface of the proximal housing 304B that have an increased friction co-efficient, e.g. rubber, silicone, or the like, or combinations thereof. As shown, the gripping feature 308 is disposed on a flared portion 303B of the proximal housing 304B, however other configurations of gripping features are also contemplated. Often a user can be wearing gloves when manipulating the needle hub 203 and the increased diameter (d1) of the needle hub 203, the flared portion(s) 303, and/or gripping feature(s) 308 can facilitate manipulation of the needle hub 203 even with gloves on.

In an embodiment, the locking mechanism 340 can be transitioned from the locked configuration to the unlocked configuration by sliding the proximal housing 304B relative to the distal housing 304A, along a longitudinal axis. For example, a user can grasp the proximal housing 304B and slide proximally away from the distal housing along the longitudinal housing to activate one or more cantilever systems that can transition the locking mechanism from the locked configuration to the unlocked configuration. In the unlocked configuration the biasing member 366 can urge the overtube 364 distally to the extended position, as described herein. As will be appreciated, the distal flared portion 303A and the proximal flared portion 303B can facilitate grasping the respective distal housing 304A and proximal housing 304B and sliding longitudinally apart, as described herein.

As shown in FIG. 8D, in an embodiment, the biasing member 366 is configured to prevent proximal movement of the overtube 364 from the extended position to prevent retraction of the overtube 364 and prevent accidental needle stick injuries. In an embodiment, the needle hub 203 can include an abutment 368 configured to abut against the overtube 364, or portion thereof, to prevent proximal movement of the overtube 364 from the extended position to prevent retraction of the overtube 364 and prevent accidental needle stick injuries.

In an exemplary method of use, as shown in FIGS. 7A-8D, an access assembly 309 can be provided, as described herein. The access assembly 309 can be coupled with an intraosseous access system 100, configured to drive the needle 204 through a bone cortex 80 and access a medullary cavity 90.

As shown in FIG. 8A, prior to insertion of the needle 204, the access assembly 309 can include an overtube 364 disposed in the retracted position and retained in the retracted position by the locking mechanism 340. As shown in FIG. 8B, the access assembly can be rotated by the driver 101 to drill the needle 204 through the skin 70 and surface tissues 75 to the bone cortex 80. The driver 101 can continue to drill the needle 204 through the bone cortex 80 and a distal portion of the overtube 364 can be inserted through the skin 70 and surface tissues 75 until the stepped portion 254 abuts against a surface of the bone cortex 80, preventing any further distal movement of the access assembly 309.

In an embodiment, prior to insertion of the needle 204, the overtube 364 can be biased towards the extended position. The needle 204 and overtube 364 can be advanced through the surface tissues 70, 75 until a distal tip of the overtube 364 contacts the bone cortex 80. The driver 101 can be activated to drill the needle 204 through the bone cortex 80. As the needle 204 advances, the overtube 364 can transition towards the retracted position.

In an embodiment, the distal surface 306 of the needle hub 203 can abut against the skin surface. As noted, the distal housing 304A can be configured to contact the skin surface and remain substantially stationary while allowing the needle 204 and/or proximal housing 304B to continue to rotate. Advantageously, then distal housing 308A can prevent friction burns, or similar trauma between the needle hub 203 and the skin surface 70.

In an embodiment, the distal surface 306 can contact the skin surface 70 prior to the stepped portion 254 contacting the bone cortex 80, or prior to the overtube 364 fully transitioning to the retracted position. As noted, the distal housing 304A can be slidably engaged with the needle hub 203 and configured to allow the needle 204 to continue to advance distally while the distal housing 304A rests on a skin surface 70. Advantageously, this can prevent the soft tissues 70, 75 from being compressed between the distal face 306 and the bone cortex 80 and stabilizes the needle hub 203 with the skin surface 70. In an embodiment, the distal housing 304A configured as such, can allow a stabilizing device to be attached to the needle hub 203 or the distal housing 304A to further stabilize the needle assembly 202 relative to the skin surface 70. Optionally, when the overtube 364 has fully transitioned to the retracted configuration, the locking mechanism can be configured to automatically retain the overtube 364 in the retracted position.

As shown in FIGS. 8C-8D, once the medullary cavity 90 has been accessed and the procedure is complete, the needle assembly 202 can be withdrawn proximally. Prior to removal of the needle 204, or after removal of the needle 204 from the insertion site, the needle hub 203 can be actuated to transition a locking mechanism 340 from the lock configuration to the unlocked configuration. In an embodiment, the proximal housing 304B can be rotated either clockwise or anticlockwise relative to the distal housing 304A to actuate the needle hub 203. In an embodiment, the proximal housing 304B can be slid longitudinally either proximally or distally relative to the distal housing 304A to actuate the needle hub 203. It will be appreciated that other configurations of actuating the needle hub 203 such as push buttons, levers, or the like are also contemplated.

With the locking mechanism 340 in the unlocked configuration, the overtube biasing member 366 can urge the overtube 364 distally and transition the overtube 364 from the retracted position to the extended position, either as the needle 204 is withdrawn from the insertion site, or optionally, after the needle is withdrawn from the insertion site. In an embodiment, the biasing member 366 can maintain the overtube 364 in the extended configuration to prevent accidental needle stick injuries. In an embodiment, the needle hub 203 can further include an abutment 368 configured to engage the overtube 364, or portion thereof, and maintain the overtube 364 in the extended configuration to prevent accidental needle stick injuries.

Advantageously, embodiments disclosed herein provide a change in needle outer diameter that is abrupt enough to substantial increase resistance to insertion. This change in insertion resistance indicates the needle tip is correctly placed. In an embodiment, the change in resistance prevents the needle from being inserted past the outer diameter step. This removes any subjective assessment as to when to stop advancing the needle. Accordingly, embodiments can be deployed by users who don't have specialized training or regular practice at placing intraosseous devices. This is especially important since placing intraosseous devices often occur in emergency situations where users may not have specialized training or regular practice, yet need to quickly access a medullary cavity for vascular access.

While some particular embodiments have been disclosed herein, and while the particular embodiments have been disclosed in some detail, it is not the intention for the particular embodiments to limit the scope of the concepts provided herein. Additional adaptations and/or modifications can appear to those of ordinary skill in the art, and, in broader aspects, these adaptations and/or modifications are encompassed as well. Accordingly, departures may be made from the particular embodiments disclosed herein without departing from the scope of the concepts provided herein. 

What is claimed is:
 1. A needle assembly for an intraosseous access system, comprising: a needle supported by a needle hub and extending to a distal tip; and a stepped increase in diameter disposed on an outer surface of the needle at a predetermined distance from the distal tip, the stepped increase in diameter configured to penetrate a skin surface and abut against a bone cortex.
 2. The needle assembly according to claim 1, wherein the predetermined distance is configured to allow the distal tip to extend through the bone cortex and into a medullary cavity of a bone.
 3. The needle assembly according to claim 1, wherein the stepped increase in diameter is formed integrally with the needle.
 4. The needle assembly according to claim 1, wherein a distal surface of the stepped increase in diameter extends perpendicular to a longitudinal axis of the needle.
 5. The needle assembly according to claim 1, wherein a distal surface of the stepped increase in diameter extends at an angle to a longitudinal axis of the needle to define a tapered shape.
 6. The needle assembly according to claim 1, wherein the needle defines a lumen having a first needle lumen diameter disposed distally of the stepped increase in diameter, and a second needle lumen diameter disposed proximally of the stepped increase in diameter, the second needle lumen diameter being larger than the first needle lumen diameter.
 7. The needle assembly according to claim 6, further including a third needle lumen diameter disposed proximally of the second needle lumen diameter, the third needle lumen diameter being less than the second needle lumen diameter to define a bulged portion in the needle.
 8. The needle assembly according to claim 6, further including an obturator disposed within the needle lumen, an outer diameter of the obturator being equal to, or less than, the first needle lumen diameter.
 9. The needle assembly according to claim 1, further including an overtube engaged with an outer surface of the needle, a distal tip of the overtube defining a portion of the stepped increase in diameter.
 10. The needle assembly according to claim 9, wherein a longitudinal length of the overtube is less than a longitudinal length of a shaft of the needle, the overtube being adhered to the outer surface of the needle to form a collar.
 11. The needle assembly according to claim 9, wherein the overtube is slidably or rotatably engaged with the needle.
 12. The needle assembly according to claim 9, wherein the overtube includes a metal, alloy, plastic, polymer, composite, or carbon-based composite material.
 13. The needle assembly according to claim 9, wherein the overtube includes a first material, and a second material different from the first material.
 14. The needle assembly according to claim 13, wherein the first material is a relatively softer material and can elastically or plastically deform, the second material is a harder material and can be resistant to any elastic or plastic deformation.
 15. The needle assembly according to claim 13, wherein the overtube is formed of concentric tubes including a first tube formed of one of the first material or the second material and disposed adjacent the needle, and a second tube disposed on an outer surface of the first tube and formed of one of the first material or the second material.
 16. The needle assembly according to claim 13, wherein the overtube is formed of adjacent tubes including a first tube formed of the first material and disposed distally of a second tube formed of the second material.
 17. The needle assembly according to claim 13, wherein a first portion of the overtube is formed the first material and extends annularly about the needle between 1° and 359°, and a second portion of the overtube is formed of the second material and extends annularly about the needle between 1° and 359°.
 18. The needle assembly according to claim 9, wherein the distal tip of the overtube is configured to blunt and increase in diameter on contact with a surface of the bone cortex.
 19. The needle assembly according to claim 1, wherein a proximal end of the overtube abuts against the needle hub to prevent further longitudinal movement of the distal tip of the needle.
 20. The needle assembly according to claim 1, wherein a first diameter of the needle hub is between 1 cm and 3 cm.
 21. The needle assembly according to claim 20, wherein the needle hub includes a flared portion extending to a second diameter, the second diameter being greater than the first diameter.
 22. The needle assembly according to claim 1, wherein the needle hub includes a proximal housing slidably or rotatably engaged with a distal housing.
 23. The needle assembly according to claim 22, wherein the needle hub includes a biasing member configured to bias the distal housing towards a proximal position relative to the proximal housing.
 24. The needle assembly according to claim 22, wherein the distal housing includes a distal face configured to engage a skin surface.
 25. The needle assembly according to claim 9, wherein the overtube is slidably engaged with the needle between a retracted position and an extended position.
 26. The needle assembly according to claim 25, wherein the distal tip of the overtube extends distally of the distal tip of the needle in the extended position.
 27. The needle assembly according to claim 25, further including an overtube biasing member configured to bias the overtube towards the extended position.
 28. The needle assembly according to claim 25, further including a locking mechanism configured to retain the overtube in the retracted position when in a locked configuration.
 29. The needle assembly according to claim 28, further including an actuator configured to transition the locking mechanism between the locked configuration and an unlocked configuration.
 30. The needle assembly according to claim 29, wherein the actuator includes rotating or sliding the proximal housing relative to the distal housing.
 31. The needle assembly according to claim 27, wherein the overtube biasing member is configured to prevent the overtube from transitioning from the extended position to the retracted position.
 32. The needle assembly according to claim 25, further including an abutment configured to engage the overtube in the extended position and prevent the overtube transitioning from the extended position to the retracted position.
 33. The needle assembly according to claim 1, wherein one of the needle or the overtube includes graduated markings.
 34. A method of accessing a medullary cavity, comprising: penetrating a bone cortex with a distal tip of a needle, the needle including a stepped increase in outer diameter disposed at a predetermined distance from the distal tip, the predetermined distance being greater than a thickness of the bone cortex; abutting the stepped increase in outer diameter against a surface of the bone cortex to prevent further distal advancement of the distal tip; and accessing the medullary cavity.
 35. The method according to claim 34, further including withdrawing an obturator from a lumen of the needle until a distal tip of the obturator is proximal of a stepped increase in diameter of the lumen to allow a proximal blood flow to be observed and confirm medullary access.
 36. The method according to claim 34, wherein an overtube is slidably or rotatably engaged with the needle, a distal surface of the overtube defining a portion of the stepped increase in outer diameter.
 37. The method according to claim 36, further including abutting a proximal end of the overtube against a needle hub to prevent further distal advancement of the distal tip of the needle.
 38. The method according to claim 34, further including abutting a distal surface of a distal housing of a needle hub against a skin surface, the distal housing slidably or rotatably engaged with a proximal housing to allow the distal tip to continue to advance distally to access the medullary cavity.
 39. The method according to claim 38, further including biasing the distal housing towards a distal position relative to the proximal housing.
 40. The method according to claim 36, further including transitioning the overtube between a retracted position, where a distal surface of the overtube is disposed at a predetermined distance from the distal tip of the needle, and an extended position where a distal surface of the overtube is disposed distally of the distal tip of the needle.
 41. The method according to claim 40, further including biasing the overtube to the extended position.
 42. The method according to claim 40, further including locking the overtube in the retracted position.
 43. The method according to claim 40, further including sliding or rotating the proximal housing relative to the distal housing to unlock the overtube and transition the overtube from the retracted position to the extended position.
 44. The method according to claim 40, further including engaging an abutment with a portion of the overtube to prevent the overtube transitioning from the extended position to the retracted position. 